The background of this invention relates to various shredding, tearing, cutting and grinding devices which process small pieces of bulk materials, such as pieces of rubber tires, into crumb-sized particles. Shredding devices are generally known which process large pieces of bulk materials.
An early patent issued to Klagsbrunn, U.S. Pat. No. 2,546,860, teaches a high speed centrifugal mill having a rotating drum having a sieve disposed on its peripheral edge with grinding tools disposed in said drum. It was used for grinding corn. Each tool disclosed had a three-edged profile and a helical pitch which allowed the mill to operate more smoothly because the striking surfaces of the centrifugal tool members did not operate along their entire length at the same moment.
U.S. Pat. No. 4,394,983, issued to Ulsky for a tire shredder assembly, has a stationary rack in opposition to a rotary cutting assembly. This device is specifically for the purpose of reducing tires to small pieces or chunks with a minimum production of fines and powdery material.
The Ehrlick et al. device, U.S. Pat. No. 3,561,303, employs a series of reciprocating or oscillating knives which co-act with a stationary anvil to shear tire moving across the anvil into diamond-shaped particles. A later patent issued to Ehrlick et al., U.S. Pat. No. 4,052,013, relates to a tire shredding device employing a pair of side-by-side parallel and generally cylindrical shredding drums, said drum defined by a series of axially spaced apart circular cutting disks.
U.S. Pat. No. 4,520,963, issued to Grebe et al., discloses a method for continuously cutting materials such as tires employs a centrifugal technique with fast rotating knives.
U.S. Pat. No. 4,714,201 issued to Rouse et al. teaches an apparatus and method for used tire processing including a method for monitoring the electrical load on the dram motor to reduce overloads. Reference therein is made to a plastics granulator manufactured by the Cumberland Engineering Company, a division of Leesona Corporation. Leesona is the assignee of numerous U.S. Patents including the following. U.S. Pat. Nos. 3,960,334; 4,106,708; 4,171,778; and 4,206,882. U.S. Pat. No. 3,960,334 relates to a size reduction apparatus having cutting means disposed laterally on a plurality of rotor plates and cooperating bed knives. The design for the cutting means disposed laterally on a plurality of rotor plates and plates are disclosed respectively in U.S. Pat. Nos. 4,106,708 and 4,206,882. U.S. Pat. No. 4,171,778, discloses the granulator rotor comprising a longitudinally oriented shaft having at least a plurality of longitudinally spaced plates that have a plurality of corners, said plates extending radially outwardly from said shaft so as to define a plurality of open box-like material receiving pockets.
Of further note are two foreign patents from the Soviet Union. Soviet Union Patent Number SU 1444-158A discloses a worn-out tire grinder for rubber reclamation having a driven cutting rotor plus fixed knives and springloaded grating for production of rubber crumb. The blade design is shown in FIG. 7. Soviet Union Patent Number SU 937-255 discloses a tire shredder for reclamation having a unique slicing knife (7) (powered rotor with exchangeable pins) and a secondary shredding rotor (15) which is not detailed in the drawing and presumably of known design.
The principal disadvantages are that the devices above fail to provide a suitable device for handling multi-grade material comminuting applications without frequent downtime resulting from jamming and time lost for replacement of cutting means. High speed centrifugal mills create these maintenance difficulties, consume considerable power and wear. Multi-shaft devices necessarily develop sizeable clearances to accommodate differences in expansion.